csky: fix syscache.c fallthrough warning

stable inclusion
from stable-5.10.50
commit 3483e1a41ca0e7be090b5134d1aff4b291a4ad53
bugzilla: 174522 https://gitee.com/openeuler/kernel/issues/I4DNFY

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3483e1a41ca0e7be090b5134d1aff4b291a4ad53

--------------------------------

[ Upstream commit 0679d29d ]

This case of the switch statement falls through to the following case.
This appears to be on purpose, so declare it as OK.

../arch/csky/mm/syscache.c: In function '__do_sys_cacheflush':
../arch/csky/mm/syscache.c:17:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   17 |   flush_icache_mm_range(current->mm,
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   18 |     (unsigned long)addr,
      |     ~~~~~~~~~~~~~~~~~~~~
   19 |     (unsigned long)addr + bytes);
      |     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../arch/csky/mm/syscache.c:20:2: note: here
   20 |  case DCACHE:
      |  ^~~~

Fixes: 997153b9 ("csky: Add flush_icache_mm to defer flush icache all")
Signed-off-by: NRandy Dunlap <rdunlap@infradead.org>
Signed-off-by: NGuo Ren <guoren@kernel.org>
Cc: linux-csky@vger.kernel.org
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/csky/mm/syscache.c

@@ -17,6 +17,7 @@ SYSCALL_DEFINE3(cacheflush,
 		flush_icache_mm_range(current->mm,
 				(unsigned long)addr,
 				(unsigned long)addr + bytes);
+		fallthrough;
 	case DCACHE:
 		dcache_wb_range((unsigned long)addr,
 				(unsigned long)addr + bytes);